The long-term objective of this project is to define and analyze the cellular interactions and molecular mechanisms involved in the regulation of collagen metabolism during tissue repair. This objective will be met by biochemically characterizing fibroblast subpopulations derived from normal dermis, scar, and keloids with respect to collagen synthesis, collagenase expression and TGFbeta receptor number and affinities. These studies test the hypothesis that fibrosis is the result of a selection of fibroblast subpopulations capable of producing increased amounts of collagen. In addition, ongoing studies will be completed to identify the collagen-producing monocytes observed during the early phase of wound repair. This specific population of cells will then be eliminated from the wound site to determine its physiological significance during tissue repair. In other studies, the amount of mRNA for collagens, fibronectin, collagenase and TGFbeta will be quantitated in normal and biologically compromised rat wounds to examine transcriptional control mechanisms during tissue repair. This information will be correlated with the actual expression of these proteins as quantitated using Western blot analysis of wound fluid and tissue extracts as well as immunohistochemical localization. In addition, collagenase will be quantitated to determine the role of collagen degradation in the net amount of collagen deposited in a wound site. The amount of collagenase mRNA will then be correlated with enzyme activity to analyze the mechanism of enzyme regulation. Keloid explants will be placed onto athymic nude mice to study collagen metabolism in vivo using oxygen-18 labeling techniques. This will allow a study of the dynamics of keloid pathogenesis in vivo and provide initial data for eventual in vivo human studies. This animal model should also prove useful for evaluation of pharmacologic agents to treat keloids. The probable role of the mast cell and tumor necrosis factor (TN-F) in keloid formation will be examined both in the athymic nude mouse model as well as in cell culture. The net result of these studies will be a better understanding of the molecular mechanisms which regulate normal wound repair and how these regulatory events are altered in abnormal repair.